Vitamin K is one of the four fat-soluble vitamins, the others being vitamins A, D and E. There are five forms of the vitamin, with the two naturally occurring forms being K-1, also known as phylloquinone, and K-2, also known as menaquinone. It was discovered in 1929 by Henrik Dam and dubbed as Koagulationsvitamin, because it was observed that animals fed a diet devoid of this vitamin had impaired blood clotting.
Functions
Vitamin K is crucial for blood to clot. The coagulation pathways are complex and require several factors to function efficiently. The role of vitamin K is to react with particular proteins and make them bind with calcium ions. Subsequently, these proteins are activated and the pathway proceeds to the next steps and ultimately causes blood to clot.
Vitamin K is also critical to bone health. According to "Introduction to Human Nutrition," vitamin K's involvement in bone health is through regulating the activity of osteoclasts, which are cells responsible for bone demineralization, and through activation of osteocalcin, a protein found in bone.
Sources
According to the "Manual of Dietetic Practice," bacteria in the colon can synthesize part of the amount of vitamin K required by humans. The chief food sources of vitamin K are green leafy vegetables such as spinach, kale, Brussels sprouts, broccoli, parsley and lettuce. The amount of the vitamin in these foods that can be absorbed by humans is increased if these foods are consumed with some fat. Animal foods containing vitamin K are meats, eggs and dairy.
Deficiency
Deficiency of vitamin K results in impaired clotting and this can cause gum bleeding, heavy menstrual bleeding, nose bleeding, easy bruising and anemia. Persons deficient in this vitamin also exhibit bone problems such as loss of bone, an increased risk of osteoporosis and an increased likelihood of fractures.
Toxicity and Drug Interactions
No toxicity symptoms have been reported with high intakes of vitamin K from foods and supplements. The exception is a synthetic form of the vitamin called menadione or K-3, which has been shown to be potentially toxic and has been banned by the Food and Drug Administration.
Anticoagulant medicine, such as warfarin, is prescribed to persons with an increased risk of unwanted clotting. Such medicine works by interfering with vitamin K metabolism. It is thus essential that if you are taking anticoagulant medicine, you should discuss your vitamin K intake with a health professional. Some cholesterol-lowering drugs and antibiotics can also affect your vitamin K status: the former through decreased absorption of the vitamin from foods and the latter through the killing of gut bacteria and thus decreasing the amount synthesized in the colon.
References
- "Introduction to Human Nutrition, 2nd Edition"; Gibney MJ et al.; 2009
- "Manual of Dietetic Practice, 4th Edition"; T. Briony and J. Bishop; 2007
Member Comments